CNT-TIM fabrication on aluminium alloy substrates

Vertically aligned carbon nanotube (VACNT) arrays have been extensively investigated as thermal interface materials (TIMs) for microelectronic packages and LED solid state lighting packages. For these applications, large scale CNT synthesis on metal substrates is needed. However, growing high quality VACNT arrays on commercial grade Al alloy substrates with good uniformity and alignment remains a challenge. A simple synthesis process needs to be developed and optimized before CNT-TIM can be commercialized. In this thesis, a vacuum enhanced thermal CVD process is presented, to grow well aligned dense CNT arrays with uniform heights on Al6063 substrates. Instead of using PECVD, we introduced a vacuum environment into the common thermal CVD process. Systematic investigations are conducted to obtain the most favorable synthesis parameters. Two catalyst systems, solution based catalyst and E-beam evaporated catalyst, are explored. For the solution based catalyst, the effects of spin coating speed and storage time of the catalyst solution to the CNT synthesis results are studied. For the E-beam evaporated catalyst, pretreatment process of the catalyst is demonstrated to play a crucial role. The other parameters, such as C2H2 flow rate, catalyst thickness, etc. are also optimized. The E-beam evaporated catalyst is finnally chosen to grow the VACNT arrays on Al6063 substrates with uniform heights. To demonstrate the application of a VACNT array as a TIM, its thermal contact resistance was evaluated by a measurement equipment designed based on American Society for Testing and Material (ASTM) D5470 standard. The resulting VACNT-TIM grown on Al6063 substrates utilizing an E-beam evaporated Fe film catalyst provides a thermal contact resistance as low as 14.6 mm2·K/W, which is less than 20% of that of commercial silver epoxy.

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Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2010